“First I'm applying a bit of eyeshadow.”

You're a makeup artist. You're putting eye makeup on a customer, and explaining what you're doing. You say:

First I'm applying a bit of eyeshadow.

first

In this example, the speaker uses "first". Here's the difference between "first" and "at first":

• "First" is used to explain the order of doing things.

  First chop the onions, green peppers, and carrots. Put them all in a bowl and the oil, garlic, soy sauce, and a pinch of salt and pepper.

• "At first" is most often used to express the difference between how something used to be and how it is now:

  At first I was nervous, but as time went on I got more and more comfortable, to the point that now I actually enjoy it.

apply (makeup)

To "apply" makeup means to put it on someone (yourself or someone else).

The word "apply" sounds technical, so you would use it in situations like when you're giving someone instructions. The person in the example above uses "apply" because she's a professional makeup artist. She's speaking to a customer, so she wants to sound professional. In normal speech, use "put on" instead of "apply":

First I'm putting some eyeshadow on you.

You can also "apply" things other than makeup:

• Apply a cream or ointment to a cut on your skin.
• Apply sunscreen.
• Apply glue to something that you're trying to stick together.
• Apply a wood-sealing liquid to the wood on your porch.

a bit of (something)

"A bit" means the same thing as "a little". It's just a bit more formal.

eyeshadow

Eyeshadow is a type of makeup. It's a powder that people use to color their eyelids. Here are a few other types of makeup:

• Eyeliner is used to draw a dark area around your eyes.
• Mascara is put on your eyelashes to make them look longer.
• Lipstick makes your lips look a different color.
• Lip gloss makes your lips look shiny.